The present invention relates to a light beam scanning device, and more particularly to a light beam scanning device for applying a synchronizing light beam via a light deflector and an image-forming optical system to a reference grating plate to generate a synchronizing signal and for applying a scanning light beam from the light deflector to an object to scan the object for reading an image or the like from or recording an image or the like on the image based on the synchronizing signal.
There is known an image scanning reading/reproducing system for applying a light beam to scan a recording medium with image information recorded thereon to photoelectrically read the recorded image information for thereby producing an image signal, and modulating a light beam with the image signal and scanning another recording medium such as a photographic photosensitive medium or the like with the modulated light beam to form a visible image thereon.
For accurate reproduction of the image information, a synchronizing signal is generated each time the light beam for reading the recorded image information is deflected a certain interval, and the recorded information is photoelectrically read under the control of the generated synchronizing signal. When recording the image information, a synchronizing signal is also produced for controlling the modulation of the light beam and application thereof to the other recording medium.
One known light beam scanning device is illustrated in FIG. 1 of the accompanying drawings, the device having a means for generating such a synchronizing signal. The illustrated light beam scanning device scans a stimulable phosphor sheet S carrying recorded image information with a laser beam L to photoelectrically reads the recorded image information. When a certain phosphor is exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, for example, the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy. The phosphor exhibiting such a property is referred to as a "stimulable phosphor", and the stimulable phosphor sheet S is a sheet having a layer of such stimulable phosphor.
In the light beam scanning device, a laser beam L emitted from a laser oscillating tube 2 is deflected in the direction of the arrow A by a polygon mirror 4 to pass through a scanning lens 6. The laser beam L is then divided by a half-silvered mirror 8 into a scanning laser beam L.sub.1 and a scanning laser beam L, which go in different directions that are about 90.degree. spaced from each other.
The scanning laser beam L.sub.1 reflected by the mirror 8 scans the stimulable phosphor sheet S in a main scanning direction (indicated by the arrow B) upon rotation of the polygon mirror 4. The stimulable phosphor sheet S is fed in an auxiliary scanning direction (indicated by the arrow C) by a sheet feed mechanism (not shown). Therefore, the scanning laser beam L.sub.1 scans the entire surface of the stimulable phosphor sheet S two-dimensionally. In response to application of the scanning laser beam L.sub.1, the stimulable phosphor sheet S emits light in an intensity proportional to the image information recorded thereon. The emitted light is then applied to a photomultiplier 12 through a light guide 10 with its light entrance end disposed over the stimulable phosphor sheet S along the main scanning line thereon. The light received by the photomultiplier 12 is converted thereby into an electric signal, which will be displayed on a display unit such as a CRT or recorded on a recording medium such as a magnetic tape.
The synchronizing laser beam L, that has passed through the mirror 8 falls on a reference grating plate 16 of a synchronizing signal generator 14, and is applied through a cylindrical light collecting bar 18 disposed behind the reference grating plate 16 to light sensors 20a, 20b mounted on the opposite ends, respectively, of the light collecting bar 18. The reference grating plate 16 has typically an array or linear pattern 22 of alternate slits and bars along the direction in which the synchronizing laser beam L.sub.2 sweeps. Therefore, the synchronizing laser beam L.sub.2 which positionally corresponds to the scanning laser beam L.sub.1 is applied as a pulsed light signal to the light sensors 20a, 20b. As a result, the light sensors 20a, 20b produce a synchronizing signal from the applied pulsed light signal, which is employed to accurately read the image information from the stimulable phosphor sheet S.
In the conventional light beam scanning device, the laser beam L emitted from the common laser oscillating tube 2 is applied to the half-silvered mirror 8 to produce the scanning laser beam L.sub.1 and the synchronizing laser beam L.sub.2. In order to apply the synchronizing laser beam L.sub.2 accurately to the reference grating plate 16 under the same conditions as the scanning laser beam L.sub.1 is applied to the stimulable phosphor sheet S, the distance between the mirror 8 and the reference grating plate 16 should be equal to the distance between the mirror 8 and the stimulable phosphor sheet S. Therefore, the synchronizing signal generator 14 including the reference grating plate 16 projects outwardly, making the light beam scanning device large in size.